1. Field of the Invention
The invention relates to a battery control system including an engine, a secondary battery used as a driving power source, and an external charging unit that charges the secondary battery using an external power supply, and also relates to a vehicle including the battery control system.
2. Description of the Related Art
In recent years, an externally chargeable electric vehicle, such as a so-called plug-in electric vehicle, on which a secondary battery that can be charged with an external power supply is installed as a driving power source, and a so-called hybrid electric vehicle on which an engine as well as the secondary battery is installed as a driving power source are in practical use. Japanese Patent Application Publication No. 2003-18756 describes calculating the internal resistance of a secondary battery installed on an electric vehicle when the secondary battery is put on charge.
In the meantime, it is necessary to control the engine and the secondary battery in the plug-in hybrid electric vehicle on which the secondary battery and the engine are installed as driving power sources, so as to stabilize the running performance of the vehicle, unlike the electric vehicle using only the secondary battery as the driving power source. It is, however, to be noted that the secondary battery degrades with use. Therefore, in the plug-in hybrid electric vehicle, the control for stabilizing the running performance of the vehicle cannot be appropriately performed on the secondary battery and the engine, unless the current condition of degradation of the secondary battery is grasped with high accuracy. As a result, a problem may arise in running of the vehicle, or the secondary battery may further degrade.